1. Field of the Invention
The invention relates to a switch valve.
2. Description of the Related Art
Conventionally, an automatic transmission used in a vehicle such as an automobile or the like has a variable speed gear provided with a planetary gear unit and the like. The variable speed gear is typically provided with a plurality of frictional engagement elements such as a clutch, a brake and the like. Further, the automatic transmission used in a vehicle is structured so as to selectively output a rotation from gear elements such as a sun gear, a ring gear, a carrier and the like in the planetary gear unit to achieve a plurality of shifting speeds by engaging and disengaging each of the frictional engagement elements in accordance with a predetermined combination.
Each of the frictional engagement elements is engaged and disengaged by operating a hydraulic servo in a hydraulic circuit. The hydraulic servo is provided with a hydraulic servo drum having an outer peripheral wall and an inner peripheral wall, and an annular piston slidably fitted within the hydraulic servo drum and the like. The hydraulic servo is structured so as to move the annular piston by supplying and discharging an oil with respect to an apply oil chamber formed between the hydraulic servo drum and the annular piston, thus engaging and disengaging the frictional engagement elements arranged in such a manner as to oppose to the annular piston.
Further, various kinds of solenoid valves, switch valves and the like are arranged in the hydraulic circuit. A predetermined switch valve is switched by turning on and off a solenoid of a predetermined solenoid valve. A hydraulic pressure is supplied to and discharged from the hydraulic servo connected to the switch valve.
For the automatic transmission having the structure disclosed above, in the case where it is intended to achieve a certain shifting speed, the structure is made such that one or more predetermined frictional engagement elements are engaged. However, when a failure or an abnormality occurs in the solenoid valve and the frictional engagement element (which is not required to be engaged) is engaged, an interlock is generated in the variable speed gear.
Accordingly, as disclosed in Japanese Patent Nos. 2689421, 2715420 and 2917272, a hydraulic circuit structured is provided in which when the hydraulic pressure is going to be supplied to the hydraulic servo in the frictional engagement element (which is not required to be engaged), a predetermined switch valve is switched by the hydraulic pressure so as to prevent the hydraulic pressure from being supplied to the hydraulic servo and prevent the interlock from being generated in the variable speed gear.
In this case, the switch valve is provided with a cylinder chamber formed in a valve body, and a spool arranged within the cylinder chamber so as to freely move forward and backward. A plurality of lands are also formed in the spool. Further, in a structure in which a diameter of a predetermined land is made different from a diameter of another land, a sleeve is arranged within the cylinder chamber and the structure is made such that the predetermined land moves forward and backward along the sleeve. In this case, when each of axes in the spool, the cylinder chamber and the sleeve is shifted, there is a risk that a failure in sliding is generated between the spool and the valve body. Therefore, the structure is made such that the spool is separated into a plunger provided with a land moved forward and backward along the sleeve, and a spool portion provided with another land.
FIG. 2 is a cross sectional view showing a main portion of a conventional switch valve.
In FIG. 2, reference numeral 150 denotes a switch valve, reference numeral 151 denotes a valve body, reference numeral 152 denotes a cylinder chamber formed in the valve body 151, and reference numeral 153 denotes a spool arranged within the cylinder chamber 152 so as to freely move forward and backward. The spool 153 is provided with a plunger 155 having a land 154, and a spool portion 156 arranged so as to freely abut against the plunger 155 and having a plurality of lands (not shown). The land 154 and another land (not shown) are formed so that their diameters are made different from each other. In this configuration, an area in which the land 154 is exposed to the hydraulic pressure and an area in which another land is exposed to the hydraulic pressure are different from each other.
A sleeve 161 is fitted and inserted within the cylinder chamber 152. The sleeve 161 is prevented from coming off by a sleeve retainer 162. A signal oil chamber 165 is formed between the plunger 155 and the sleeve 161. Further, an input port 166 is formed in the signal oil chamber 165. A control hydraulic pressure is supplied via the input port 166.
The plunger 155 moves forward and backward along the sleeve 161, while an outer peripheral surface of the land 154 and an inner peripheral surface of a land portion g in the sleeve 161 move in a sliding motion. Further, the spool portion 156 moves forward and backward along the cylinder chamber 152, while an outer peripheral surface of said another land and an inner peripheral surface of the land portion in the valve body 151 move in a sliding motion.
In a normal non-failure state, the switch valve 150 adopts a left half position. However, when a failure occurs, the switch valve 150 adopts a right half position. At this time, a predetermined hydraulic pressure is prevented from being supplied to the hydraulic servo to prevent the frictional engagement element from being engaged.
However, the conventional switch valve 150 is configured to prevent the interlock from being generated in the variable speed gear. The switch valve 150 is thus operated only when failure occurs. The switch valve 150 is not operated and is placed at a predetermined position at the normal, non-failure state.
Accordingly, during engine operation, the vibration generated by a pulsation of the hydraulic pressure or the like in the hydraulic circuit is transmitted to the plunger 155. This condition causes fretting, i.e., vibration without slide motions, to be generated in the plunger 155 at the predetermined position. In this configuration a stepped wear portion 167 formed along a shape of a corner portion of the land 154 is formed on the inner peripheral surface of the land portion g. When foreign materials 168 such as wear powders or the like, accumulate in the stepped wear portion 167 and enter a portion between the land 154 and the sleeve 161 when failure occurs, it is difficult or almost impossible to smoothly move the plunger 155, causing driver discomfort.
Further, because the outer peripheral surface of the plunger 155 and the inner peripheral surface of the land portion g are scratched by the foreign materials 168, and durability of the switch valve 150 is decreased.
It is an objective of the invention to solve the problems in the conventional switch valve by providing a switch valve which can increase durability without causing driver discomfort when a failure occurs.
To accomplish the above objective in various exemplary embodiments according to this invention, a switch valve is provided with a spool having a spool portion arranged so as to freely move forward and backward. The switch valve further includes at least one land and a plunger arranged so as to freely abut against the spool portion. The plunger is also provided with a land. The switch valve further includes a spool surrounding portion surrounding the spool. The spool surrounding portion also includes a plurality of land portions corresponding to the respective lands.
In the above configuration the spool selectively adopts a position at a normal state and a position at a fail state. Further, in the position at the normal state, at least one corner portion of the land in the plunger protrudes from an end portion of the corresponding land portion.
In this case, at the position at the normal non-failure state, at least one corner portion in the land of the plunger protrudes from the end portion of the corresponding land portion.
Accordingly, because the stepped wear portion is not formed on the inner peripheral surface of the land portion, foreign materials, such as the wear powders or the like, do not enter the portion between the outer peripheral surface of the land and the inner peripheral surface of the land portion at a time when the failure occurs. As a result, it is possible to smoothly move the plunger without causing driver discomfort.
Further, because the outer peripheral surface of the land and the inner peripheral surface of the land portion are not scratched by the foreign materials, it is possible to increase durability of the switch valve.
In another exemplary embodiment, the switch valve of this invention includes a spool surrounding portion made by a cylinder chamber formed in a valve body.
In yet another exemplary embodiment, the switch valve of this invention includes a spool surrounding portion made by a cylinder chamber and a sleeve arranged in the cylinder chamber.